This invention relates to a method and apparatus for the application of moisture to the gummed flaps of envelopes or the like, and is more in particular directed to the rapid moistening of gummed flaps in a high speed mailing machine, wherein the envelopes are moved into a moistening station by one drive device, and withdrawn from the moistening station by another drive device.
U.S. Pat. No. 3,911,862 discloses a moistening system for envelope flaps wherein a pair of fixed nozzles are aligned to selectively spray water against an envelope flap, in dependence upon the output of a sensor arranged to detect the location of the edge of the flap in the plane perpendicular to the direction of motion of the envelope that passes through the nozzles. Thus, a first of the nozzles is controlled to spray water at the flap if the sensor does not detect the envelope flap, and the other of the nozzles sprays water if the sensor does detect the envelope. In this arrangement, another sensor is arranged to control the supply of water to the nozzles when the leading edge of the envelope passes a determined position, and to inhibit the supply of water to the nozzles when the trailing edge of the envelope has passed that position.. In an alternative arrangement, instead of employing two (or more) nozzles, the reference discloses the movement of a single nozzle between two end positions by means of a solenoid, under the control of the output of the flap edge position sensor, or under the control of feedback from a contoured template.
The system disclosed in the above reference, however, is not adapted to the high speed moistening of envelopes, especially since consideration is not given to the rapid change of the position of the moistener nozzle required for high speed movement of the envelopes. In addition, the above system turns the spray from the nozzle on and off solely in response to the sensing of the leading and trailing edges of the envelope, independently of the configuration of the flap, and is not adapted to compensation for response times of various movable elements of the system or control of the moisture necessary for properly moistening the envelope flaps.
In accordance with a feature of the invention, a method for moistening the flap of an envelope is provided, comprising directing a spray of a liquid at an envelope flap, via a nozzle, along a given locus in a given plane, driving an envelope at first and second spaced apart positions in a first direction in the given plane upstream and downstream, respectively, of the nozzle, providing position signals that are a function of the position of the edge in the plane, moving the nozzle in response to the first signals in a direction substantially parallel to the plane for moistening the flap at positions thereof, providing first and second signals corresponding to the speed of the envelope as it is being moved at the first and second positions, respectively. The step of moving the nozzle comprises controlling the position of the nozzle as a function of the first signals for moistening a first portion of the flap of the envelope, and controlling the position of the nozzle as a function of the second signals for moistening a second portion of the flap of the envelope.